By Meeri Kim
The pervasive glow of electronic devices may be an impediment to a good night’s sleep. That’s particularly noticeable now, when families are adjusting to early wake-up times for school. Teenagers can find it especially hard to get started in the morning. For nocturnal animals, it spurs activity. For daytime species such as humans, melatonin signals that it’s time to sleep.
As lamps switch off in teens’ bedrooms across America, the lights from their computer screens, smartphones and tablets often stay on throughout the night. These devices emit light of all colors, but it’s the blues in particular that pose a danger to sleep. Blue light is especially good at preventing the release of melatonin, a hormone associated with nighttime.
Ordinarily, the pineal gland, a pea-size organ in the brain, begins to release melatonin a couple of hours before your regular bedtime. The hormone is no sleeping pill, but it does reduce alertness and make sleep more inviting.
However, light — particularly of the blue variety — can keep the pineal gland from releasing melatonin, thus warding off sleepiness. You don’t have to be staring directly at a television or computer screen: If enough blue light hits the eye, the gland can stop releasing melatonin. So easing into bed with a tablet or a laptop makes it harder to take a long snooze, especially for sleep-deprived teenagers who are more vulnerable to the effects of light than adults.
During adolescence, the circadian rhythm shifts, and teens feel more awake later at night. Switching on a TV show or video game just before bedtime will push off sleepiness even later even if they have to be up by 6 a.m. to get to school on time.

Maggie Fox NBC News
Every cell in your body has a little clock ticking away in it, researchers reported on Sunday. And while most of you is aging in a coordinated way, odd anomalies that have the researchers curious: Your heart may be “younger” than the rest of your tissues, and a woman’s breasts are older.
Tumors are the oldest of all, a finding reported in the journal Genome Biology that might help scientists better understand cancer, explain why breast cancer is so common and help researchers find better ways to prevent it.
Less surprising, but intriguing: embryonic stem cells, the body’s master cells, look just like newborns with a biological age of zero.
The new measurements might be useful in the search for drugs or other treatments that can turn back the clock on aging tissue and perhaps treating or preventing diseases of aging, such as heart disease and cancer, says Steve Horvath, a professor of genetics at the David Geffen School of Medicine at UCLA.
“The big question is whether the biological clock controls a process that leads to aging,” Horvath said.
Horvath looked at a genetic process called methylation. It’s a kind of chemical reaction that turns on or off stretches of DNA. All cells have the entire genetic map inside; methylation helps determine which bits of the map the cells use to perform specific functions.

By GRETCHEN REYNOLDS
If you consider yourself to be a born morning person or an inveterate night owl, there is new research that supports your desire to wake up early or stay up late. Each of us has a personal “chronotype,” or unique circadian rhythm, says Till Roenneberg, a professor of chronobiology at Ludwig Maximilian University in Munich and one of the world’s experts on sleep. In broad strokes, these chronotypes are usually characterized as early, intermediate or late, corresponding to people who voluntarily go to bed and wake early, at a moderate hour or vampirishly late. If you are forced to wake up earlier than your body naturally would, you suffer from what Roenneberg calls “social jet lag.”
People with an early chronotype may do well with a 7 a.m. workday rising time, but others do not. Sleeping out of sync with your innate preferences can be detrimental to your health, especially for late chronotypes, who tend to be the most at odds with typical work schedules. A study conducted by the National Institutes of Health and published in March in PLOS ONE found that obese adults with late chronotypes tended to eat larger meals, develop more sleep apnea and have higher levels of stress hormones and lower levels of HDL, or “good,” cholesterol than obese people with other chronotypes.
Their chronotype may also have contributed to weight gain in the first place, Roenneberg says. Research has shown that a single hour of social jet lag, the mismatch between your chronotype and your schedule, increases your risk for obesity by about 33 percent. In a study published in June in Chronobiology International, late-night chronotypes gained more weight during their freshman years at college than other new students did, even though college is one of the best fits for night owls.
Copyright 2013 The New York Times Company